1. Field of the Invention
The present invention relates to a resolver stator. In particular, the present invention relates to a resolver stator which uses a soft resin, such as silicone, instead of an epoxy which has been used in a known technology for a varnish for fixing a stator coil, thereby preventing the stator coil and wires between the stator coil and terminals from disconnection caused by cracks and the like of the varnish, which are produced when used in an environment in which temperature varies in a wide range.
2. Description of the Related Art
In a known resolver stator, a stator coil wound around magnetic poles of the resolver stator is generally impregnated with a varnish using an epoxy, the varnish being dried and cured, for fixing the stator coil to the resolver stator.
A melted resin covers the overall stator coil including terminals and is cured.
The known resolver stator having the above configuration has problems described below.
When the resolver stator is used in an environment in which temperature varies in a wide range, cracks which cause disconnection of the stator coil are produced due to degradation at high temperature and expansion/contraction caused by variation in temperature because the stator coil is affixed by using a varnish including a hard epoxy.
In manufacturing a known stator coil, the varnish must be cured at a high temperature; therefore, a temperature-controlled bath is necessary and manufacturing costs are increased because of the temperature control.
Wire ends of the stator coil are exposed from the resin which covers the overall stator coil including terminals. Therefore, there is a risk in that the wire ends of the stator coil are broken at exposed parts thereof by vibration or expansion/contraction applied to the stator coil, which causes disconnection.
Accordingly, it is an object of the present invention to provide a resolver stator which is improved by using a soft resin, such as silicone, thereby preventing the stator coil and wires between the stator coil and terminals from disconnection caused by cracks and the like of the varnish, which are produced when used in an environment in which temperature varies in a wide range.
To the end, according to an aspect of the present invention, a resolver stator comprises a stator coil including a plurality of winding portions each wound around a magnetic pole via ring-shaped insulation caps, the stator coil being impregnated with a liquid or melted resin and fixed to the magnetic poles by curing the resin. The resin is softer than an epoxy. The resin may be silicone. A peripheral part of one of the ring-shaped insulation caps may be provided with a plurality of terminals. Wire ends of the stator coil may be each wound around one of the plurality of terminals such that each wire end and the terminal form a winding-connecting part. The wire end and the terminal may be fixed to each other by soldering or fusing at one portion of the winding-connecting part and be independent from each other at the remaining portion of the winding-connecting part such that the wire end disposed in the remaining portion of the winding-connecting part is formed as a free wire end. The free wire end may be wound around the terminal at least once. The free wire end may be wound around the terminal a plurality of times. The free wire end may have a resilient function and slack.
The resolver stator according to the present invention offers advantages described below.
The stator coil is fixed to the magnetic poles of the resolver stator via a resin, such as silicone, which is softer than that of an epoxy which is used for a known resolver stator. The resin such as silicone has elasticity even when the temperature at which the resolver stator is used varies in a wide range. Therefore, disconnection in the stator coil is avoided, and the resolver stator can be reliably used regardless of operational environment.
Since the resin such as silicone is elastic, it is not necessary to accurately control the amount of application of the resin, and the apparatus to be used for impregnation of the resin is not complex, whereby manufacturing costs are reduced.
Since the resin is cured by natural drying, temperature control is not necessary for curing, whereby manufacturing costs are reduced.
A part of the wire end of the stator coil wound around the terminal provided at the ring-shaped insulation cap is not fixed to the terminal and has a slack so as to have a resilient function. Therefore, deformation due to thermal expansion, vibration, and the like can be absorbed, whereby disconnection can be avoided, and a reliable resolver stator is obtainable.